The present invention relates to pipe joints, and more particularly to pipe joints suitable, for example, for use in manufacturing semiconductors of which extremely high cleanliness is required.
The present inventor has already proposed a pipe joint suited, for example, to use in fabricating semiconductors of which extremely high cleanliness is required. With reference to FIG. 6, the proposed pipe joint comprises a pair of tubular joint members 1, 2, an annular gasket 3 interposed between abutting end faces of the joint members 1, 2 and threaded means for joining the joint members 1, 2, the abutting end faces of the joint members 1, 2 being formed with annular seal projections 37, 38 respectively, so that when the threaded means is completely tightened up, recesses corresponding to the respective seal projections 37, 38 are created in end faces of the gasket 3, with respective inner peripheries 1a, 2a of the abutting end faces of the joint members 1, 2 becoming approximately flush with an inner periphery 3a of the gasket 3. The pipe joint is characterized in that each of the seal projections 37, 38 has a sectional contour which comprises a circular-arc portion 37b (38b) extending radially outward from the abutting end face, and a straight portion 37a (38a) extending from the circular-arc portion 37b (38b) (see JP-A-32984/1997). Referring to the same drawing, the abutting end faces have respective inner flat portions 15, 16 formed inwardly of the seal projections 37, 38, and respective outer flat portions 17, 18 positioned outwardly of the projections 37, 38. Indicated at 9 and 10 are overtightening preventing annular ridges formed at the outer peripheries of the respective abutting end faces.
The pipe joint described has no liquid trapping cavity, is unlikely to develop in the inner periphery of the gasket creases which would permit deposition of dirt and further enables the worker, while tightening the threaded member, to perceive an altered reaction which indicates the completion of tightening. Thus, the pipe joint has features suitable for use in manufacturing semiconductors. However, the joint has the following problem. While such pipe joints as assembled once are frequently disassembled and assembled again, the joint shown in FIG. 6 has the drawback that the gasket 3 is difficult to remove from the joint members 1, 2 for disassembly because when the gasket 3 is to be moved axially relative to the first and second joint members 1, 2, the straight portions 37a, 38a of the seal projections 37, 38 biting in the gasket 3 give increased friction against the movement of the gasket.